<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8" />
    <title>子元素的margin-top会传递给父元素（margin垂直外边距合并）,可以通过给子元素创建BFC来解决，或者通过增加子父元素padding-top</title>
    <style type="text/css">

        .show {
            margin: 0px auto;
            width: 200px;
            height: 200px;
            overflow: hidden;
            background-color: #999999;
        }
    </style>
</head>

<body>

    <div class="show">
        <h2 style="margin-bottom:50px">crystal</h2>
        <h2 style="margin-top:50px">tets</h2>
    </div>

</body>

</html>